ADAM-8, a metalloproteinase, drives acute allergen-induced airway inflammation

A jack of all trades - ADAM8 as a signaling hub in inflammation and cancer

As a member of the family of A Disintegrin And Metalloproteinases (ADAM) ADAM8 is preferentially expressed in lymphatic organs, immune cells, and tumor cells. The substrate spectrum for ADAM8 proteolytic activity is not exclusive but is related to effectors of inflammation and signaling in the tumor microenvironment. In addition, complexes of ADAM8 with extracellular binding partners such as integrin β-1 cause an extensive intracellular signaling in tumor cells, thereby activating kinase pathways with STAT3, ERK1/2, and Akt signaling, which causes increased cell survival and enhanced motility. The cytoplasmic domain of ADAM8 harbors five SRC homology-3 (SH3) domains that can potentially interact with several proteins involved in actin dynamics and cell motility, including Myosin 1F (MYO1F), which is essential for neutrophil motility. The concept of ADAM8 thus involves immune cell recruitment, in most cases leading to an enhancement of inflammatory (asthma, COPD) and tumor (including pancreatic and breast cancers) pathologies. In this review, we report on available studies that qualify ADAM8 as a therapeutic target in different pathologies. As a signaling hub, ADAM8 controls extracellular, intracellular, and intercellular communication, the latter one mainly mediated by the release of extracellular vesicles with ADAM8 as cargo. Here, we will dissect the contribution of different domains to these distinct ways of communication in several pathologies. We conclude that therapeutic targeting attempts for ADAM8 should consider blocking more than a single domain and that this requires a thorough evaluation of potent molecules targeting ADAM8 in an in vivo setting.

Role for the metalloproteinase ADAM28 in the control of airway inflammation, remodelling and responsiveness in asthma

Background

Asthma is characterized by morphological modifications of the airways (inflammation and remodelling) and bronchial hyperresponsiveness. Mechanisms linking these two key features of asthma are still poorly understood. ADAM28 (a disintegrin and metalloproteinase 28) might play a role in asthma pathophysiology. ADAM28 exists as membrane-bound and soluble forms and is mainly expressed by lymphocytes and epithelial cells.

Methods

ADAM28^-/- mice and ADAM28^+/+ counterparts were sensitized and exposed to ovalbumin (OVA). Airway responsiveness was measured using the flexiVent^® system. After sacrifice, bronchoalveolar lavage (BAL) was performed and lungs were collected for analysis of airway inflammation and remodelling.

Results

The expression of the soluble form of ADAM28 was lower in the lungs of OVA-exposed mice (as compared to PBS-exposed mice) and progressively increased in correlation with the duration of allergen exposure. In lungs of ADAM28^-/- mice exposed to allergens, the proportion of Th2 cells among CD 4 + cells and the number of B cells were decreased. Bronchial responsiveness was lower in ADAM28^-/- mice exposed to allergens and similar to the responsiveness of sham-challenged mice. Similarly, features of airway remodelling (collagen deposition, smooth muscle hyperplasia, mucous hyperplasia) were significantly less developed in OVA-exposed ADAM28^-/- animals in sharp contrasts to ADAM28^+/+. In addition, we report the first evidence of ADAM28 RNA expression by lung fibroblasts and we unveil a decreased capacity of lung fibroblasts extracted from OVA-exposed ADAM28^-/- mice to proliferate as compared to those extracted from OVA-exposed ADAM28^+/+ suggesting a direct contribution of this enzyme to the modulation of airway remodelling.

Conclusion

These results suggest that ADAM28 might be a key contributor to the pathophysiology of asthma.

NOD2 Signaling Circuitry during Allergen Sensitization Does Not Worsen Experimental Neutrophilic Asthma but Promotes a Th2/Th17 Profile in Asthma Patients but Not Healthy Subjects

Nucleotide-binding oligomerization domain 2 (NOD2) recognizes pathogens associated with the development of asthma. Moreover, NOD2 adjuvants are used in vaccine design to boost immune responses. Muramyl di-peptide (MDP) is a NOD2 ligand, which is able to promote Th2/Th17 responses. Furthermore, polymorphisms of the NOD2 receptor are associated with allergy and asthma development. This study aimed to evaluate if MDP given as an adjuvant during allergen sensitization may worsen the development of Th2/Th17 responses. We used a mouse model of Th2/Th17-type allergic neutrophil airway inflammation (AAI) to dog allergen, with in vitro polarization of human naive T cells by dendritic cells (DC) from healthy and dog-allergic asthma subjects. In the mouse model, intranasal co-administration of MDP did not modify the AAI parameters, including Th2/Th17-type lung inflammation. In humans, MDP co-stimulation of allergen-primed DC did not change the polarization profile of T cells in healthy subjects but elicited a Th2/Th17 profile in asthma subjects, as compared with MDP alone. These results support the idea that NOD2 may not be involved in the infection-related development of asthma and that, while care has to be taken in asthma patients, NOD2 adjuvants might be used in non-sensitized individuals.

ADAMDEC1 accelerates GBM progression via activation of the MMP2-related pathway

The ADAM (a disintegrin and metalloprotease) gene-related family including ADAM, ADAMTS, and ADAM-like decysin-1 has been reported to play an important role in the pathogenesis of multiple diseases, including cancers (lung cancer, gliomas, colorectal cancer, and gastrointestinal cancer). However, its biological role in gliomas remains largely unknown. Here, we aimed to investigate the biological functions and potential mechanism of ADAMDEC1 in gliomas. The mRNA and protein expression levels of ADAMDEC1 were upregulated in glioma tissues and cell lines. ADAMDEC1 showed a phenomenon of “abundance and disappear” expression in gliomas and normal tissues in that the higher the expression of ADAMDEC1 presented, the higher the malignancy of gliomas and the worse the prognosis. High expression of ADAMDEC1 was associated with immune response. Knockdown of ADAMDEC1 could decrease the proliferation and colony-forming ability of LN229 cells, whereas ADAMDEC1 overexpression has opposite effects in LN229 cells in vitro. Furthermore, we identified that ADAMDEC1 accelerates GBM progression via the activation of the MMP2 pathway. In the present study, we found that the expression levels of ADAMDEC1 were significantly elevated compared with other ADAMs by analyzing the expression levels of ADAM family proteins in gliomas. This suggests that ADAMDEC1 has potential as a glioma clinical marker and immunotherapy target.

Sex-Biased Gene Expression of Mesobuthus martensii Collected from Gansu Province, China, Reveals Their Different Therapeutic Potentials

The scorpions, named Mesobuthus martensii, commonly called Quanxie (全蝎) in Chinese, have been widely used as one of the animal medicines for more than 1,000 years because of the strong toxicity of their venoms. Meanwhile, scorpions are sexually dimorphic in appearance, and many exhibit traits associated with sex-biased gene expression, including maternal care, mating competition, female mating choices, ecology, and even venom composition and lethality. This study aims to explore the differences in composition of the venom of scorpions of different sex using the method of transcriptomics. Whole de novo transcriptomes were performed on the samples of M. martensii captured from Gansu Province to identify their sex-biased gene expression. The conserved CO-1 sequences of the captured samples matched that of M. martensii. A total of 8,444 (35.15%), 7,636 (31.78%), 8,510 (35.42%), 7,840 (32.63%), 9,980 (41.54%), and 11,829 (49.23%) unigenes were annotated with GO, KEGG, Pfam, Swissprot, eggNOG, and NR databases. Moreover, a total of 43 metalloproteases, 40 potassium channel toxins, 24 phospholipases, 12 defensins, 10 peroxiredoxins, 9 cysteine proteinase inhibitors, 7 serine protease inhibitors, 6 sodium channel toxins, 2 NDBPs, 1 calcium channel toxin, 1 waprin-like peptide, 1 antibacterial peptide, 1 antimicrobial peptide, and 1 anticoagulant peptide were screened out. With the fold change of 2 and 0.5, p value < 0.01, and q value < 0.05 as thresholds, a total of 41 out of 157 (26.11%) toxin-related unigenes had significant differential expression, and this ratio was much higher than the ratio of differentially expressed unigenes out of all annotated ones (8.84%). Of these differentially expressed toxins, 28 were upregulated and occupied the majority, up to 68.30%. The female scorpions showed more upregulated unigenes that annotated with toxins and had the potential to be used as more effective therapeutic drugs. In addition, this method of omics can be further used as a useful way to identify the difference between female and male toxic animals.

Expression of the Metalloproteinase ADAM8 Is Upregulated in Liver Inflammation Models and Enhances Cytokine Release In Vitro

Acute and chronic liver inflammation is driven by cytokine and chemokine release from various cell types in the liver. Here, we report that the induction of inflammatory mediators is associated with a yet undescribed upregulation of the metalloproteinase ADAM8 in different murine hepatitis models. We further show the importance of ADAM8 expression for the production of inflammatory mediators in cultured liver cells. As a model of acute inflammation, we investigated liver tissue from lipopolysaccharide- (LPS-) treated mice in which ADAM8 expression was markedly upregulated compared to control mice. In vitro, stimulation with LPS enhanced ADAM8 expression in murine and human endothelial and hepatoma cell lines as well as in primary murine hepatocytes. The enhanced ADAM8 expression was associated with an upregulation of TNF-α and IL-6 expression and release. Inhibition studies indicate that the cytokine response of hepatoma cells to LPS depends on the activity of ADAM8 and that signalling by TNF-α can contribute to these ADAM8-dependent effects. The role of ADAM8 was further confirmed with primary hepatocytes from ADAM8 knockout mice in which TNF-α and IL-6 induction and release were considerably attenuated. As a model of chronic liver injury, we studied liver tissue from mice undergoing high-fat diet-induced steatohepatitis and again observed upregulation of ADAM8 mRNA expression compared to healthy controls. In vitro, ADAM8 expression was upregulated in hepatoma, endothelial, and stellate cell lines by various mediators of steatohepatitis including fatty acid (linoleic-oleic acid), IL-1β, TNF-α, IFN-γ, and TGF-β. Upregulation of ADAM8 was associated with the induction and release of proinflammatory cytokines (TNF-α and IL-6) and chemokines (CX3CL1). Finally, knockdown of ADAM8 expression in all tested cell types attenuated the release of these mediators. Thus, ADAM8 is upregulated in acute and chronic liver inflammation and is able to promote inflammation by enhancing expression and release of inflammatory mediators.

Genetic association of ADAM33 polymorphisms with childhood asthma in Chinese Han population: A case-control study

To explore the association of a disintegrin and metalloprotease 33 (ADAM33) polymorphisms with childhood asthma susceptibility, we conducted this case-control study.In this case-control study, we selected 96 asthma children and 86 healthy children to conduct the genotyping of ADAM33 polymorphisms through polymerase chain reaction-direct sequencing (PCR-DS). Hardy-Weinberg equilibrium (HWE) status in the control group was detected adopting chi-square test. Frequency differences of genotypes, alleles, and haplotypes were compared by chi-square test between the case and control groups. Linkage disequilibrium (LD) between polymorphisms was checked using Haploview software. Association intensity of the polymorphisms with the disease risk was assessed by odds ratio (OR) and 95% confidence interval (95%CI).The frequency of rs678881 GA genotype was obviously higher in cases than in controls (P = .03) and the carriage of this genotype conferred higher risk of asthma among children than GG genotype (OR = 2.03, 95%CI = 1.05-3.91). However, neither rs2280089 nor rs2853209 polymorphism was significantly associated with the risk of childhood asthma. Strong LD was found among rs678881, rs2280089 and rs2853209, and haplotype GGT was distinctly associated with the risk of asthma in children (OR = 0.28, 95%CI = 0.13-0.57).ADAM33 rs678881 polymorphism is significantly correlated with increased susceptibility to asthma in Chinese Han children. Besides, haplotype GGT among the 3 polymorphisms was obviously associated with decreased risk of childhood asthma.

ADAM8 in invasive cancers: links to tumor progression, metastasis, and chemoresistance

Ectodomain shedding of extracellular and membrane proteins is of fundamental importance for cell-cell communication in neoplasias. A Disintegrin And Metalloproteinase (ADAM) proteases constitute a family of multifunctional, membrane-bound proteins with traditional sheddase functions. Their protumorigenic potential has been attributed to both, essential (ADAM10 and ADAM17) and 'dispensable' ADAM proteases (ADAM8, 9, 12, 15, and 19). Of specific interest in this review is the ADAM proteinase ADAM8 that has been identified as a significant player in aggressive malignancies including breast, pancreatic, and brain cancer. High expression levels of ADAM8 are associated with invasiveness and predict a poor patient outcome, indicating a prognostic and diagnostic potential of ADAM8. Current knowledge of substrates and interaction partners gave rise to the hypothesis that ADAM8 dysregulation affects diverse processes in tumor biology, attributable to different functional cores of the multidomain enzyme. Proteolytic degradation of extracellular matrix (ECM) components, cleavage of cell surface proteins, and subsequent release of soluble ectodomains promote cancer progression via induction of angiogenesis and metastasis. Moreover, there is increasing evidence for significance of a non-proteolytic function of ADAM8. With the disintegrin (DIS) domain ADAM8 binds integrins such as β1 integrin, thereby activating integrin signaling pathways. The cytoplasmic domain is critical for that activation and involves focal adhesion kinase (FAK), extracellular regulated kinase (ERK1/2), and protein kinase B (AKT/PKB) signaling, further contributing to cancer progression and mediating chemoresistance against first-line therapies. This review highlights the remarkable effects of ADAM8 in tumor biology, concluding that pharmacological inhibition of ADAM8 represents a promising therapeutic approach not only for monotherapy, but also for combinatorial therapies.

Chromosome 17q21 Genes ORMDL3 and GSDMB in Asthma and Immune Diseases

Chromosome 17q21 contains a cluster of genes including ORMDL3 and GSDMB, which have been highly linked to asthma in genome-wide association studies. ORMDL3 is localized to the endoplasmic reticulum and regulates downstream pathways including sphingolipids, metalloproteases, remodeling genes, and chemokines. ORMDL3 inhibits serine palmitoyl-CoA transferase, the rate-limiting enzyme for sphingolipid biosynthesis. In addition, ORMDL3 activates the ATF6α branch of the unfolded protein response which regulates SERCA2b and IL-6, pathways of potential importance to asthma. The SNP-linking chromosome 17q21 to asthma is associated with increased ORMDL3 and GSDMB expression. Mice expressing either increased levels of human ORMDL3, or human GSDMB, have an asthma phenotype characterized by increased airway responsiveness and increased airway remodeling (increased smooth muscle and fibrosis) in the absence of airway inflammation. GSDMB regulates expression of 5-LO and TGF-β1 which are known pathways involved in the pathogenesis of asthma. GSDMB is one of four members of the GSDM family (GSDMA, GSDMB, GSDMC, and GSDMD). GSDMD (located on chromosome 8q24 and not linked to asthma) has emerged as a key mediator of pyroptosis. GSDMD is a key component of the NLPR3 inflammasome and is required for its activation. GSDMD undergoes proteolytic cleavage by caspase-1 to release its N-terminal fragment, which in turn mediates pyroptosis and IL-1β secretion. Chromosome 17q21 has not only been linked to asthma but also to type 1 diabetes, inflammatory bowel disease, and primary biliary cirrhosis suggesting that future insights into the biology of genes located in this region will increase our understanding of these diseases.

The metalloproteinase ADAM8 promotes leukocyte recruitment in vitro and in acute lung inflammation

Alveolar leukocyte recruitment is a hallmark of acute lung inflammation and involves transmigration of leukocytes through endothelial and epithelial layers. The disintegrin and metalloproteinase (ADAM) 8 is expressed on human isolated leukocytic cells and can be further upregulated on cultured endothelial and epithelial cells by proinflammatory cytokines. By shRNA-mediated knockdown we show that leukocytic ADAM8 is required on monocytic THP-1 cells for chemokine-induced chemotaxis as well as transendothelial and transepithelial migration. Furthermore, ADAM8 promotes α_L-integrin upregulation and THP-1 cell adhesion to endothelial cells. On endothelial cells ADAM8 enhances transendothelial migration and increases cytokine-induced permeability. On epithelial cells the protease facilitates migration in a wound closure assay but does not affect transepithelial leukocyte migration. Blood leukocytes and bone marrow-derived macrophages (BMDM) from ADAM8-deficient mice show suppressed chemotactic response. Intranasal application of LPS to mice is accompanied with ADAM8 upregulation in the lung. In this model of acute lung inflammation ADAM8-deficient mice are protected against leukocyte infiltration. Finally, transfer experiments of BMDM in mice indicate that ADAM8 exerts a promigratory function predominantly on leukocytes. Our study provides in vitro and in vivo evidence that ADAM8 on leukocytes holds a proinflammatory function in acute lung inflammation by promoting alveolar leukocyte recruitment.

IL-5-stimulated eosinophils adherent to periostin undergo stereotypic morphological changes and ADAM8-dependent migration

BACKGROUND

IL-5 causes suspended eosinophils to polarize with filamentous (F)-actin and granules at one pole and the nucleus in a specialized uropod, the "nucleopod," which is capped with P-selectin glycoprotein ligand-1 (PSGL-1). IL-5 enhances eosinophil adhesion and migration on periostin, an extracellular matrix protein upregulated in asthma by type 2 immunity mediators.

OBJECTIVE

Determine how the polarized morphology evolves to foster migration of IL-5-stimulated eosinophils on a surface coated with periostin.

METHODS

Blood eosinophils adhering to adsorbed periostin were imaged at different time points by fluorescent microscopy, and migration of eosinophils on periostin was assayed.

RESULTS

After 10 minutes in the presence of IL-5, adherent eosinophils were polarized with PSGL-1 at the nucleopod tip and F-actin distributed diffusely at the opposite end. After 30-60 minutes, the nucleopod had dissipated such that PSGL-1 was localized in a crescent or ring away from the cell periphery, and F-actin was found in podosome-like structures. The periostin layer, detected with monoclonal antibody Stiny-1, shown here to recognize the FAS1 4 module, was cleared in wide areas around adherent eosinophils. Clearance was attenuated by metalloproteinase inhibitors or antibodies to disintegrin metalloproteinase 8 (ADAM8), a major eosinophil metalloproteinase previously implicated in asthma pathogenesis. ADAM8 was not found in podosome-like structures, which are associated with proteolytic activity in other cell types. Instead, immunoblotting demonstrated proteoforms of ADAM8 that lack the cytoplasmic tail in the supernatant. Anti-ADAM8 inhibited migration of IL-5-stimulated eosinophils on periostin.

CONCLUSIONS AND CLINICAL RELEVANCE

Migrating IL-5-activated eosinophils on periostin exhibit loss of nucleopodal features and appearance of prominent podosomes along with clearance of the Stiny-1 periostin epitope. Migration and epitope clearance are both attenuated by inhibitors of ADAM8. We propose, therefore, that eosinophils remodel and migrate on periostin-rich extracellular matrix in the asthmatic airway in an ADAM8-dependent manner, making ADAM8 a possible therapeutic target.

Fine Tuning Cell Migration by a Disintegrin and Metalloproteinases

Cell migration is an instrumental process involved in organ development, tissue homeostasis, and various physiological processes and also in numerous pathologies. Both basic cell migration and migration towards chemotactic stimulus consist of changes in cell polarity and cytoskeletal rearrangement, cell detachment from, invasion through, and reattachment to their neighboring cells, and numerous interactions with the extracellular matrix. The different steps of immune cell, tissue cell, or cancer cell migration are tightly coordinated in time and place by growth factors, cytokines/chemokines, adhesion molecules, and receptors for these ligands. This review describes how a disintegrin and metalloproteinases interfere with several steps of cell migration, either by proteolytic cleavage of such molecules or by functions independent of proteolytic activity.

Interferon response factor-3 promotes the pro-Th2 activity of mouse lung CD11b+ conventional dendritic cells in response to house dust mite allergens

Very few transcription factors have been identified that are required by antigen-presenting cells (APCs) to induce T helper type 2 (Th2) responses. Because lung CD11b⁺ conventional dendritic cells (CD11b⁺ cDCs) are responsible for priming Th2 responses in house-dust mite (HDM)-induced airway allergy, we used them as a model to identify transcriptional events regulating the pro-Th2 activity of cDCs. Transcriptomic profiling of lung CD11b⁺ cDCs exposed to HDM in vivo revealed first that HDM triggers an antiviral defence-like response, and second that the majority of HDM-induced transcriptional changes depend on the transcription factor Interferon Response Factor-3 (Irf3). Validating the functional relevance of these observations, Irf3-deficient CD11b⁺ cDCs displayed reduced pro-allergic activity. Indeed, Irf3-deficient CD11b⁺ cDCs induced less Th2, more regulatory T cell, and similar Th1 differentiation in naïve CD4⁺ T cells compared to their wild-type counterparts. The altered APC activity of Irf3 CD11b⁺ cDCs was associated with reduced expression of CD86 and was phenocopied by blocking CD86 activity in wild-type CD11b⁺ cDCs. Altogether, these results establish Irf3, known mostly for its role in antiviral responses, as a transcription factor involved in the induction of Th2 responses through the promotion of pro-Th2 costimulation in CD11b⁺ DCs.

A novel peptide ADAM8 inhibitor attenuates bronchial hyperresponsiveness and Th2 cytokine mediated inflammation of murine asthmatic models

A disintegrin and metalloproteinase 8 (ADAM8) has been identified as a signature gene associated with moderate and severe asthma. Studies in mice have demonstrated that the severity of asthma can be reduced by either transgenic knock-out or by antibodies blocking ADAM8 function, highlighting ADAM8 as potential drug target for asthma therapy. Here, we examined the therapeutic effect of an ADAM8 inhibitor peptide (BK-1361) that specifically blocks cellular ADAM8 activity in ovalbumin-sensitized and challenged Balb/c mice. We found that BK-1361 (25 μg/g body weight) attenuated airway responsiveness to methacholine stimulation by up to 42%, concomitantly reduced tissue remodeling by 50%, and decreased inflammatory cells (e.g. eosinophils down by 54%)/inflammatory factors (e.g. sCD23 down by 50%)/TH2 cytokines (e.g. IL-5 down by 70%)/ADAM8-positive eosinophils (down by 60%) in the lung. We further verified that BK-1361 specifically targets ADAM8 in vivo as the peptide caused significantly reduced levels of soluble CD23 in wild-type but not in ADAM8-deficient mice. These findings suggest that BK-1361 blocks ADAM8-dependent asthma effects in vivo by inhibiting infiltration of eosinophils and TH2 lymphocytes, thus leading to reduction of TH2-mediated inflammation, tissue remodeling and bronchial hyperresponsiveness. Taken together, pharmacological ADAM8 inhibition appears as promising novel therapeutic strategy for the treatment of asthma.

8th international conference on management and rehabilitation of chronic respiratory failure: the long summaries – part 1

This paper summarizes the Part 1 of the proceedings of the 8^th International Conference on Management and Rehabilitation of Chronic Respiratory Failure, held in Pescara, Italy, on 7 and 8 May, 2015. It summarizes the contributions from numerous experts in the field of chronic respiratory disease and chronic respiratory failure. The outline follows the temporal sequence of presentations.

This paper (Part 1) includes sections regarding: Advances in Asthma and COPD Therapy (Novel Therapeutic Targets for Asthma: Proteinases, Blood Biomarker Changes in COPD Patients); The problem of Hospital Re-Admission following Discharge after the COPD Exacerbation (Characteristics of the Hospitalized COPD Patient, Reducing Hospital Readmissions Following COPD Exacerbation).

Copy number variation burden on asthma subgenome in normal cohorts identifies susceptibility markers

PURPOSE

Asthma is a complex disease caused by interplay of genes and environment on the genome of an individual. Copy number variations (CNVs) are more common compared to the other variations that disrupt genome organization. The effect of CNVs on asthma subgenome has been less studied compared to studies on the other variations. We report the assessments of CNV burden in asthma genes of normal cohorts carried out in different geographical areas of the world and discuss the relevance of the observation with respect to asthma pathogenesis.

METHODS

CNV analysis was performed using Affymerix high-resolution arrays, and various bioinformatics tools were used to understand the influence of genes on asthma pathogenesis.

RESULTS

This study identified 61 genes associated with asthma and provided various mechanisms and pathways underlying asthma pathogenesis. CCL3L1, ADAM8, and MUC5B were the most prevalent asthma genes. Among them, CCL3L1 was found across all 12 populations in varying copy number states. This study also identified the inheritance of asthma-CNVs from parents to offspring creating the latent period for manifestation of asthma.

CONCLUSIONS

This study revealed CNV burden with varying copy number states and identified susceptibility towards the disease manifestation. It can be hypothesized that primary CNVs may not be the initiating event in the pathogenesis of asthma and additional preceding mutations or CNVs may be required. The initiator or primary CNVs sensitize normal cohorts leading to an increased probability of accumulating mutations or exposure to allergic stimulating agents that can augment the development of asthma.

Sputum ADAM8 expression is increased in severe asthma and COPD

BACKGROUND

Severe asthma and chronic obstructive pulmonary disease (COPD) are chronic inflammatory airway diseases in which the mechanisms are not fully understood. A disintegrin and metalloproteinase domain 8 (ADAM8) is an enzyme expressed on most leucocytes and may be important for facilitating leucocyte migration in respiratory disease.

OBJECTIVE

To investigate ADAM8 mRNA and protein expression in asthma and COPD and its relationship between asthma severity and inflammatory phenotypes.

METHODS

Induced sputum was collected from 113 subjects with asthma (severe n = 31, uncontrolled n = 39 and controlled n = 35), 20 subjects with COPD and 21 healthy controls. Sputum ADAM8 mRNA expression was measured by qPCR, and soluble ADAM8 (sADAM8) protein was measured in the sputum supernatant by validated ELISA.

RESULTS

ADAM8 mRNA correlated with ADAM8 protein levels (r = 0.27, P < 0.01). ADAM8 mRNA (P = 0.004) and sADAM8 protein (P = 0.014) levels were significantly higher in both asthma and COPD compared with healthy controls. ADAM8 mRNA (P = 0.035) and sADAM8 protein (P = 0.002) levels were significantly higher in severe asthma compared with controlled asthma. Total inflammatory cell count (P < 0.01) and neutrophils (P < 0.01) were also elevated in severe asthmatic sputum. Although ADAM8 mRNA was significantly higher in eosinophilic and neutrophilic asthma (P < 0.001), sADAM8 did not differ between asthma inflammatory phenotypes. ADAM8 expression positively correlated with sputum total cell count and sputum neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

ADAM8 expression is increased in both severe asthma and COPD and associated with sputum total cell count and neutrophils. ADAM8 may facilitate neutrophil migration to the airways in severe asthma and COPD.

ADAM8 in asthma. Friend or foe to airway inflammation?

Airway inflammation has been suggested as the pathological basis in asthma pathogenesis. Recruitment of leukocytes from the vasculature into airway sites is essential for induction of airway inflammation, a process thought to be mediated by a disintegrin and metalloprotease 8 (ADAM8). However, there is an apparent controversy about whether ADAM8 helps or hampers transmigration of leukocytes through endothelium in airway inflammation of asthma. This review outlines the current contradictory concepts concerning the role of ADAM8 in airway inflammation, particularly focusing on the recruitment of leukocytes during asthma, and attempts to bridge the existing experimental data on the basis of the functional analysis of different domains of ADAM8 and their endogenous processing in vivo. We suggest a possible hypothesis for the specific mechanism by which ADAM8 regulates the transmigration of leukocytes to explain the disparity existing in current studies, and we also raise some questions that require future investigations.

Adam8 limits the development of allergic airway inflammation in mice

To determine whether a disintegrin and metalloproteinase-8 (Adam8) regulates allergic airway inflammation (AAI) and airway hyperresponsiveness (AHR), we compared AAI and AHR in wild-type (WT) versus Adam8(-/-) mice in different genetic backgrounds sensitized and challenged with OVA or house dust mite protein extract. OVA- and house dust mite-treated Adam8(-/-) mice had higher lung leukocyte counts, more airway mucus metaplasia, greater lung levels of some Th2 cytokines, and higher methacholine-induced increases in central airway resistance than allergen-treated WT mice. Studies of OVA-treated Adam8 bone marrow chimeric mice confirmed that leukocyte-derived Adam8 predominantly mediated Adam8's anti-inflammatory activities in murine airways. Airway eosinophils and macrophages both expressed Adam8 in WT mice with AAI. Adam8 limited AAI and AHR in mice by reducing leukocyte survival because: 1) Adam8(-/-) mice with AAI had fewer apoptotic eosinophils and macrophages in their airways than WT mice with AAI; and 2) Adam8(-/-) macrophages and eosinophils had reduced rates of apoptosis compared with WT leukocytes when the intrinsic (but not the extrinsic) apoptosis pathway was triggered in the cells in vitro. ADAM8 was robustly expressed by airway granulocytes in lung sections from human asthma patients, but, surprisingly, airway macrophages had less ADAM8 staining than airway eosinophils. Thus, ADAM8 has anti-inflammatory activities during AAI in mice by activating the intrinsic apoptosis pathway in myeloid leukocytes. Strategies that increase ADAM8 levels in myeloid leukocytes may have therapeutic efficacy in asthma.

Ectodomain shedding and ADAMs in development

Proteolytic enzymes belonging to the A Disintegin And Metalloproteinase (ADAM) family are able to cleave transmembrane proteins close to the cell surface, in a process referred to as ectodomain shedding. Substrates for ADAMs include growth factors, cytokines, chemokines and adhesion molecules, and, as such, many ADAM proteins play crucial roles in cell-cell adhesion, extracellular and intracellular signaling, cell differentiation and cell proliferation. In this Review, we summarize the fascinating roles of ADAMs in embryonic and adult tissue development in both vertebrates and invertebrates.

Control of allergen-induced inflammation and hyperresponsiveness by the metalloproteinase ADAMTS-12

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) constitute a family of endopeptidases related to matrix metalloproteinases. These proteinases have been largely implicated in tissue remodeling associated with pathological processes. Among them, ADAMTS12 was identified as an asthma-associated gene in a human genome screening program. However, its functional implication in asthma is not yet documented. The present study aims at investigating potential ADAMTS-12 functions in experimental models of allergic airways disease. Two different in vivo protocols of allergen-induced airways disease were applied to the recently generated Adamts12-deficient mice and corresponding wild-type mice. In this study, we provide evidence for a protective effect of ADAMTS-12 against bronchial inflammation and hyperresponsiveness. In the absence of Adamts12, challenge with different allergens (OVA and house dust mite) led to exacerbated eosinophilic inflammation in the bronchoalveolar lavage fluid and in lung tissue, along with airway dysfunction assessed by increased airway responsiveness following methacholine exposure. Furthermore, mast cell counts and ST2 receptor and IL-33 levels were higher in the lungs of allergen-challenged Adamts12-deficient mice. The present study provides, to our knowledge, the first experimental evidence for a contribution of ADAMTS-12 as a key mediator in airways disease, interfering with immunological processes leading to inflammation and airway hyperresponsiveness.

Nebulized anti-IL-13 monoclonal antibody Fab' fragment reduces allergen-induced asthma

IL-13 is a prototypic T helper type 2 cytokine and a central mediator of the complex cascade of events leading to asthmatic phenotype. Indeed, IL-13 plays key roles in IgE synthesis, bronchial hyperresponsiveness, mucus hypersecretion, subepithelial fibrosis, and eosinophil infiltration. We assessed the potential efficacy of inhaled anti-IL-13 monoclonal antibody Fab' fragment on allergen-induced airway inflammation, hyperresponsiveness, and remodeling in an experimental model of allergic asthma. Anti-IL-13 Fab' was administered to mice as a liquid aerosol generated by inExpose inhalation system in a tower allowing a nose-only exposure. BALB/c mice were treated by PBS, anti-IL-13 Fab', or A33 Fab' fragment and subjected to ovalbumin exposure for 1 and 5 weeks (short-term and long-term protocols). Our data demonstrate a significant antiasthma effect after nebulization of anti-IL-13 Fab' in a model of asthma driven by allergen exposure as compared with saline and nonimmune Fab fragments. In short- and long-term protocols, administration of the anti-IL-13 Fab' by inhalation significantly decreased bronchial responsiveness to methacholine, bronchoalveolar lavage fluid eosinophilia, inflammatory cell infiltration in lung tissue, and many features of airway remodeling. Levels of proinflammatory mediators and matrix metalloprotease were significantly lower in lung parenchyma of mice treated with anti-IL-13 Fab'. These data demonstrate that an inhaled anti-IL-13 Fab' significantly reduces airway inflammation, hyperresponsiveness, and remodeling. Specific neutralization of IL-13 in the lungs using an inhaled anti-IL-13 Fab' could represent a novel and effective therapy for the treatment of asthma.

Regulating inflammation: ADAM8--a new player in the game

Leukocyte recruitment to sites of inflammation proceeds in a cascade-like fashion. However, it is less clear how the complex interactions among the different adhesion molecules involved in this process are coordinately regulated. A report in this issue of the European Journal of Immunology [Eur. J. Immunol. 2011. 41: 3436-3442] shows that ADAM8 may participate in the control of the adhesion molecule P-selectin glycoprotein ligand 1. This finding suggests a new role for ADAM8 in the regulation of inflammatory processes.